KR101271991B1 - Secondary battery - Google Patents

Abstract

The present invention relates to a secondary battery capable of enhancing the adhesive force between the substrate and the active material layer by providing an intermediate layer containing a carbon material between the substrate and the active material layer. Secondary battery according to the present invention; An intermediate layer comprising a carbon material formed on the substrate; And an active material layer formed on the intermediate layer. Such a structure prevents the active material from falling off, thereby improving the performance of the battery, and by using a small amount of a binder having strong adhesion to the active material slurry, it is possible to ensure the stability of the battery.

Description

Secondary battery

The present invention relates to a secondary battery, and more particularly to a secondary battery that can improve the performance of the battery.

In general, a secondary battery is a battery that can be charged and discharged, unlike a primary battery that is not rechargeable. The secondary battery includes a positive electrode plate, a negative electrode plate, and an electrode assembly having a shape in which a separator is laminated or wound therebetween. At this time, the positive electrode plate is a form in which the positive electrode active material is coated on the positive electrode substrate, the negative electrode plate is a form in which the negative electrode active material is coated on the negative electrode substrate.

Charging and discharging of the secondary battery may be performed by moving lithium ions to the positive electrode active material or the negative electrode active material. However, the positive electrode active material and the negative electrode active material may be dropped in the manufacturing process of the secondary battery when the adhesion to the substrate is weak. Such dropping of the active material may cause defects in the bare cell, and the bare cell defect may cause many problems not only in the performance of the battery but also in the safety of the battery.
The prior art is Japanese Patent Laid-Open No. 2000-149924.

An object of the present invention is to provide a secondary battery capable of enhancing adhesion between the substrate and the active material layer by providing an intermediate layer containing a carbon material between the substrate and the active material layer.

In addition, an object of the present invention is to provide a secondary battery that can reduce the amount of the binder mixed in the active material slurry.

Secondary battery according to the present invention; An intermediate layer comprising a carbon material formed on the substrate; And an active material layer formed on the intermediate layer.

In this case, the intermediate layer may further include a binder.

The carbon material may be any one selected from the group consisting of graphite, graphene nanosheets, and graphenes.

In addition, the adhesion between the substrate and the active material layer may be formed in the range of 0.5gf / mm to 5.0gf / mm.

In addition, the thickness of the intermediate layer may be formed in the range of 0.2㎛ 5㎛.

Furthermore, the carbon material may include a crystalline region and an amorphous region.

Here, the amorphous region of the carbon material may be formed in the range of 2% to 50%.

In addition, the substrate may include a current collector of a positive electrode.

In addition, the binder may include at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyimide (PI), polyamideimide (PAI), chitosan (chitosane), and styrene-butadiene rubber (SBR).

According to the present invention, by dropping the active material by the adhesion between the substrate and the active material is prevented, it is possible to improve the reliability and life of the battery.

Moreover, according to this invention, stability of a battery can be ensured by mixing a small amount of binder with an active material slurry.

1 is a cross-sectional view showing a process of forming an intermediate layer and an active material layer on a substrate according to the present invention.
2 is a chemical structural formula of graphite.
Figure 3a is a chemical structural formula of the graphene nanosheets.
Figure 3b is a TEM (Transmission Electron Microscope, transmission electron microscope) photograph of the graphene nanosheets.
4 is a chemical structural formula of graphene.
5 is a graph showing the results of X-ray diffraction (XRD) analysis of a carbon material.
6 is a graph comparing the rate characteristics of a base plate and an electrode plate having graphene nanosheets formed thereon.
FIG. 7 is a graph comparing high lifespan characteristics of a base plate and an electrode plate having graphene nanosheets formed thereon.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to embodiments of the present invention and other details necessary for those skilled in the art to understand the present invention with reference to the accompanying drawings. However, the present invention may be embodied in various different forms within the scope of the claims, and thus the embodiments described below are merely exemplary, regardless of expression.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. It should be noted that the same components in the drawings are denoted by the same reference numerals and signs as possible even if they are shown in different drawings. In addition, the thickness and size of each layer in the drawings may be exaggerated for convenience and clarity, and may differ from actual layer thicknesses and sizes.

1 is a cross-sectional view illustrating a process of forming an intermediate layer and an active material layer on a substrate according to the present invention.

Referring to FIG. 1, a secondary battery according to the present invention includes a base 10 and an active material layer 30 formed on the base 10. The intermediate layer 20 further includes a carbon material between the substrate 10 and the active material layer 30.

Looking at the process of forming the intermediate layer 20 and the active material layer 30 on the substrate 10 according to the present invention, the substrate 10 is prepared first. At this time, the substrate 10 may be a positive electrode current collector or a negative electrode current collector formed of a conductive metal thin plate, and particularly preferably a positive electrode current collector. In general, the positive electrode current collector may be formed of aluminum (Al).

And the intermediate | middle layer 20 containing a carbon material can be formed on the base material 10. In this case, the intermediate layer 20 may further include a binder having a strong adhesive force in addition to carbon. That is, the intermediate layer 20 may be a thin film coated on the substrate 10 in the form of a mixture of carbon and a binder. Since the binder is mixed in the intermediate layer 20 as described above, the intermediate layer 20 may have improved adhesion to the substrate 10 or the active material layer 30.

In addition, the carbon material of the intermediate layer 20 may be a mixture of the crystalline region and the amorphous region. Functional groups may be formed in such amorphous regions. As a result, the amorphous region of the carbon material may further improve the binding property with the functional group in the binder than the crystalline region. For example, functional groups of the binder that can be bonded to the amorphous region include a hydroxyl group (R-OH), a carboxy group (R-COOH), an aldehyde (R-CHO), and the like. Therefore, the carbon and the binder of the intermediate layer 20 can more easily form one layer.

The amorphous region of the carbon material may be formed in the range of 2% to 50%. If the amorphous region is formed to less than 2%, there is a problem that the carbon yield is relatively reduced in the manufacturing process, the treatment cost is increased, the price is increased, and the binding with the substrate 10 is reduced. In addition, if the amorphous region is formed in excess of 50%, there is a problem in that the conductivity is decreased to increase the resistance.

Here, the carbon material may be any one selected from the group consisting of graphite, graphene nanosheets, and graphenes.

When the carbon material is formed of graphite, graphene nanosheets, or graphene, the adhesion between the substrate 10 and the active material layer 30 may be increased while improving electrical conductivity in the electrode plate. The electrical conductivity of graphite, graphene nanosheets or graphene is excellent, and when carbon is present on the substrate 10, the contact area with the active material layer 30 is increased than when only the substrate 10 is present. As a result, the increase of the contact area appears as an effect of increasing the adhesion in the electrode plate, and the electrical conductivity in the electrode plate is increased.

Here, when the carbon material is a graphene nanosheet or graphene, since the crystallinity is superior to graphite in addition to the advantages described above, there may be greater strength in terms of electrical conductivity.

In addition, the binder of the intermediate layer 20 may include at least one selected from the group consisting of polyvinylidene fluoride (PVDF), polyimide (PI), polyamideimide (PAI), chitosan (Chitosane), and styrene-butadiene rubber (SBR). Can be.

In addition, the thickness of the intermediate layer 20 in which the carbon and the binder are mixed may be formed in a range of 0.2 μm to 5 μm. When the thickness of the intermediate layer 20 is less than 0.2 μm, the adhesive force with the substrate 10 or the active material layer 30 may be reduced. In addition, when the thickness of the intermediate layer 20 is greater than 5 μm, the adhesive force with the substrate 10 or the active material layer 30 may be further increased, but the electrical conductivity tends to be lowered.

As described above, according to the present invention, the active material layer 30 is formed on the substrate 10 on which the intermediate layer 20 is formed, thereby increasing adhesion and electrical conductivity. Here, the active material layer 30 may be formed using a method of applying the active material slurry to the base material 10 or attaching the active material slurry into a sheet shape to the base material 10.

The active material layer 30 on the substrate 10 used as the positive electrode current collector may be formed using a positive electrode slurry. The positive electrode slurry may include a positive electrode active material, a conductive material, and a small amount of positive electrode binder in a solvent, and may be coated on at least one surface of the positive electrode current collector to form the active material layer 30.

Here, the positive electrode active material participates in the positive electrode chemical reaction of the lithium secondary battery to generate electrons, and the conductive material may transfer electrons generated from the positive electrode active material to the positive electrode current collector. In addition, the positive electrode binder may bind the positive electrode active material and the conductive material and maintain the mechanical strength of the positive electrode plate 11.

Lithium composite metal compounds such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi-xCoxO ₂ (0 <x> 1), and LiMnO ₂ are used as the positive electrode active material, but the material thereof is not limited thereto.

In general, carbon may be used as a negative electrode active material, but in the present invention, carbon may be used as an adhesive on the base material 10 and the active material layer 30 which are the positive electrode current collectors. As such, by forming the intermediate layer 20, two layers of the intermediate layer 20 and the active material layer 30 may be formed on the substrate 10. Thereby, the adhesiveness and electrical conductivity of the base material 10 and the active material layer 30 can be improved.

In addition, by forming the intermediate layer 20 containing carbon in the substrate 10, the resistance of the substrate 10 can be lowered, thereby securing high output and long life characteristics of the secondary battery. In addition, the substrate 10 on which the intermediate layer 20 containing carbon is formed has an excellent effect in improving the adhesion between the substrate 10 and the active material layer 30 while preserving the properties of the general substrate.

Hereinafter, the charging and discharging process of the secondary battery will be briefly described. During charging, in which electrons are provided from the charger to the negative electrode of the secondary battery, lithium ions move from the positive electrode active material to the negative electrode active material. That is, lithium ions generated from the lithium compound pass through the electrolyte and the separator and are intercalated with the negative electrode active material to charge. In addition, during discharge in which electrons are emitted through the negative electrode, lithium ions intercalated in the negative electrode active material move to the positive electrode active material. That is, the lithium ions pass through the electrolyte and the separator from the negative electrode active material and deintercalated with the lithium compound, thereby discharging.

As described above, the positive electrode active material and the negative electrode active material of the secondary battery are important materials for allowing lithium ions to move and perform charge and discharge. Therefore, such an active material should be excellent in adhesion with the substrate 10 so as not to fall off the substrate 10. In the present invention, the adhesion between the base material 10 and the active material layer 30 can be improved by forming the intermediate layer 20 containing carbon between the base material 10 and the active material layer 30.

In addition, by including the binder in the intermediate layer 20, it is possible to prevent the performance degradation of the battery due to the use of the binder in the existing active material slurry. In addition, even when the binder is included in the intermediate layer 20 than when the binder is included in the active material slurry, even if the amount of the binder is reduced, the adhesion between the substrate 10 and the active material layer 30 may be further enhanced.

Hereinafter, a method of manufacturing a secondary battery according to the present invention will be described.

The secondary battery according to the present invention first prepares a substrate 10. In addition, the intermediate layer 20 is formed by coating a mixed solution of a carbon solution and a binder solution on the substrate 10. Here, the carbon solution may be any one selected from the group consisting of graphite, graphene nanosheets, and graphene.

The mixed solution of carbon solution and binder solution can be coated using a screenprint coating method or a spray coating method.

The screenprint coating method prepares a mask in which an area to be coated with a mixed solution of a carbon solution and a binder solution is opened. Then, a mask is placed on the substrate 10. Thereafter, the mixed solution of the carbon solution and the binder solution is transferred onto the substrate 10 using a roller to the open area of the mask.

The spray coating method prepares a mask in which the area to be coated with the mixed solution of the carbon solution and the binder solution is opened. Then, a mask is placed on the substrate 10. Thereafter, a mixed solution of the carbon solution and the binder solution is sprayed. As a result, a mixed solution of a carbon solution and a binder solution may be coated on the substrate 10.

Then, the active material layer 30 is formed on the intermediate layer 20 coated with the mixed solution of the carbon solution and the binder solution.

2 is a chemical structural formula of graphite.

Referring to FIG. 2, graphite is a hexagonal crystal and has a plurality of plate-like structures. In other words, the structure of graphite has a layered structure in which six carbon rings are connected. Here, covalent bonds are formed between the carbon atoms (A) in the same layer, and are connected to the carbon atoms (B) in the other layer by weak bonding force.

3A is a chemical structural formula of graphene nanosheets.

Referring to FIG. 3A, the graphene nanosheets have a form in which the plate-shaped structure of the graphite of FIG. 2 is formed to have a thickness of 5 nm to 50 nm. That is, it is formed by breaking the bond between carbons (B) between different layers of graphite. In the case of graphene nanosheets, since the thickness is smaller than that of graphite, the graphene nanosheets have a smaller amount and can increase the electrical conductivity and the adhesion of the plate.

3B is a TEM photograph of graphene nanosheets.

As shown in FIG. 3B, the graphene nanosheets used in the present invention exist in a mixed state of the crystalline region and the amorphous region. The upper side of FIG. 3B is a crystal region, and the lower side represents an amorphous region. As such, since the crystalline region and the amorphous region are mixed, there is an advantage that the crystalline region and the amorphous region are cheaper than the carbon material forming the perfect crystal.

In addition, the amorphous region has a larger surface area because the surface is rougher than the crystal region, and when used as the intermediate layer 20 (see FIG. 1), the adhesion with the base material 10 (see FIG. 1) or the active material layer 30 (see FIG. 1). This can be increased. As described above, the functional group formed in the amorphous region may further improve the binding property with the functional group in the binder.

4 is a chemical structural formula of graphene.

Referring to Figure 4, graphene (Graphene) is an acronym created by combining 'graphene', meaning carbon, and '-ene', meaning 'unsaturated hydrocarbon'. In other words, graphene is a carbon compound, which means one layer of graphite having a plate-like structure, and has a two-dimensional shape.

In particular, when the graphene nanosheet or the graphene-containing intermediate layer 20 is coated on the substrate 10, the van der Waals attraction force may be increased. In addition, when the active material layer 30 is coated on the intermediate layer 20, which is a post-process, attractive force may also act on the contact surface between the active material layer 30 and the intermediate layer 20, thereby increasing the adhesive force.

Since the graphene nanosheets or graphenes have a flat sheet form, the contact surface is large. In addition, the graphene may form a planar triangle structure having three sp ² structures consisting of one s orbital and two p orbitals.

Table 1 shows an example in which the intermediate layer 20 is formed between the base material 10 and the active material layer 30, and a comparison when the intermediate layer 20 is not formed between the base material 10 and the active material layer 30. The adhesive force according to the example was compared.

division Middle layer presence Adhesive force (gf / mm) Example O 1.4 Comparative example X 0.4

As shown in Table 1, the case where the intermediate layer 20 is formed between the base material 10 and the active material layer 30 (an example) is less than the case where the intermediate layer 20 is not formed (comparative example). It can be seen that the adhesion between the active material layer 30 is higher. That is, the adhesive force when the intermediate layer 20 was formed was 1.4 gf / mm, whereas the adhesive force when the intermediate layer 20 was not formed was measured as 0.4 gf / mm.

When such an intermediate layer is formed, the adhesion between the substrate 10 and the active material layer 30 may be formed in a range of 0.5 gf / mm to 5.0 gf / mm. Here, when the adhesion between the base material 10 and the active material layer 30 is less than 0.5 gf / mm, foreign matters such as falling off of the electrode plate may occur in the electrode plate winding process, which may be a problem in cell safety. In addition, when the adhesion between the base material 10 and the active material layer 30 exceeds 5.0 gf / mm, the electrode plate becomes hard and there is a problem that the electrode plate material may be broken during the winding process.

5 is a graph showing the results of X-ray diffraction (XRD) analysis of a carbon material.

Referring to FIG. 5, XRD analyzes a diffraction pattern when X-rays are scattered or diffracted by projecting X-rays onto a sample. Therefore, the microstructure of the carbon material, in particular, the crystallinity can be used more accurately. In particular, according to the Scherer's equation of Equation 1, the crystal size Lc of the graphene nanosheet of FIG. 3A may be obtained.

Where L = crystallite size, B = Peak width (FWHM, Full Width at Half Maximum), λ = wavelength of x-rays θ = angle corresponding to the peak

division FWHM Two theta Crystal size (Å) Example 1 (GNS Lc) 0.56029 26.384 146 Example 2 (GNS Lc) 0.46844 26.577 174

The crystal size (Lc) of the graphene nanosheets can be obtained by substituting the values of Table 2 in Equation 1, and the crystal sizes of 146 Å and 174 Å were shown in Examples 1 and 2.

6 is a graph comparing the rate characteristics of the base plate and the electrode plate on which the graphene nanosheets are formed.

Referring to FIG. 6, the residual capacity ratios of the electrode plates having the active material layer formed on the substrate and the electrode plates having the graphene nanosheets and the active material layer formed on the substrate were compared.

Here, the charge / discharge rate is a unit for predicting or indicating the current value under various use conditions and the possible use time of the secondary battery when charging or discharging the battery. The calculation of the current value according to the charge / discharge rate is based on the charge or discharge current. Calculate the charge / discharge current value by dividing the value by subtracting the unit of battery rated capacity.

Charge / discharge rate (A) = charge / discharge current (A) / rated capacity of battery

In addition, the usage time can be converted or predicted based on the following expression based on the capacity expressed relative to the rated capacity under the current condition calculated from the charge / discharge rate.

Operating time (h) = expression capacity (Ah) / discharge current (A)

here,

Residual Capacity Ratio (%) = Active Material Residual Capacity [mAh / g] / Active Material Initial Capacity [mAh / g] × 100

When comparing the graphene plate (GNS_Al) coated with graphene nanosheets on the aluminum substrate according to the present invention and the electrode plate (Ref_Al) using an aluminum substrate, the rate characteristic is almost similar. That is, the graphene nanosheet coated electrode plate according to the present invention not only improves the electrical conductivity and adhesion, but also has the property of lowering the resistance and exhibits the same rate characteristics as the electrode plate using the conventional aluminum substrate. Able to know.

FIG. 7 is a graph comparing high-rate life characteristics of a base plate and an electrode plate having graphene nanosheets formed thereon.

As shown in Figure 7, the experimental conditions of high rate life is the cycle life results of continued charging and discharging at 4C-rate. When the graphene nanosheet and the active material layer (GNS_Al) on which the active material layer is formed on the aluminum substrate according to the present invention and the electrode plate (Ref_Al) in the state where the active material layer is formed on the aluminum substrate, high-rate life characteristics have a similar form. In other words, it exhibits a high rate characteristic in which the residual capacity ratio decreases as the charge / discharge cycle is repeated.

However, when comparing the residual capacity ratio after 90 charge / discharge cycles, the residual capacity ratio of the present invention (GNS_Al) represents approximately 61%, and the residual capacity ratio of the comparative material (Ref_Al) represents approximately 52%. . Through this, it can be seen that the electrode plate (GNS_Al) according to the present invention exhibits a higher rate of life characteristics than the comparative material (Ref_Al).

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be apparent to those skilled in the art that various modifications may be made without departing from the scope of the present invention.

The scope of the present invention is defined by the following claims. The scope of the present invention is not limited to the description of the specification, and all variations and modifications falling within the scope of the claims are included in the scope of the present invention.

10: substrate
20: middle layer
30: active material layer

Claims (14)

materials;
An intermediate layer including a carbon material formed on the substrate; And
An active material layer formed on the intermediate layer;
The carbon material includes a graphene nano sheet,
The carbon material includes a secondary battery. The method of claim 1,
The intermediate layer further comprises a binder, the secondary battery is present in a mixed state with the carbon material. delete The method of claim 1,
Adhesion between the substrate and the active material layer is a secondary battery formed in the range of 0.5gf / mm to 5.0gf / mm. The method of claim 1,
The thickness of the intermediate layer is a secondary battery formed in the range of 0.2㎛ 5㎛. delete The method of claim 1,
An amorphous region of the carbon material is formed in the range of 2% to 50%. The method of claim 1,
The substrate is a secondary battery comprising a current collector of the positive electrode. The method of claim 2,
The binder includes at least one selected from the group consisting of Polyvinylidene Flouride (PVDF), Polyimide (PI), Polyamideimide (PAI), Chitosane, and Styrene-Butadiene Rubber (SBR). Preparing a substrate;
Coating a mixed solution of a carbon solution and a binder solution on the substrate; And
Forming an active material on the mixed solution;
The carbon solution includes a graphene nanosheet,
The carbon solution is a method of manufacturing a secondary battery comprising an amorphous region. The method of claim 10,
In the coating step, the carbon solution and the binder solution is coated using a screen print coating method of manufacturing a secondary battery. The method of claim 10,
In the coating step, the carbon solution and the binder solution is coated using a spray coating method. The method of claim 10,
In the coating step, the carbon solution and the binder solution is a secondary battery manufacturing method of coating in a mixed state with each other. delete

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